Introduction.—Chiral interaction, also known as nonreciprocal coupling, refers to the asymmetric coupling amplitude between the left and right objects [1]}, such as the asymmetric hopping amplitude between two nearest sites in Hatano-Nelson model [2]}. It has been successfully implemented to realize the non-Hermitian skin effect in one-dimensional systems, featured by a macroscopic number of eigenstates piling up at one end [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}. These states turn out to be topologically exceptional as showing anomalous bulk-boundary correspondence that may be characterised by generalized
Brillouin zone [4]}, [5]}, and are promising for applications such as topological funneling of light [8]}.
